A variety of body lumens are subject to undesired strictures or narrow regions. For example, blood vessels can be blocked or narrowed by atherosclerosis, while esophageal strictures can arise from individual anatomical differences, or from diseases such as connective tissue disorder.
Procedures for dilating or enlarging such strictures or narrowed regions often entail the use of a balloon dilation catheter. In general, such catheters include a deflated balloon which can be positioned across a particular stricture or narrowed region, and which is then inflated with an inflation fluid in order to widen the lumen without trauma to the wall of the lumen.
Conventional dilation balloons fall into high, medium, and low pressure ranges. Low pressure balloons are those that have burst pressures below 6 atmospheres (ATM) (6.1×105 Pascals). Medium pressure balloons are those that have burst pressures between 6 and 15 ATM (6.1×105 and 1.2×106 Pa). High pressure balloons are those that have burst pressures above 15 ATM (1.2×106 Pa) and as high as 30 ATM. The term “burst pressure” refers to the maximum pressure which can be slowly applied to the balloon (at a specific temperature and for a specified amount of time (e.g., seconds or minutes)) without causing it to rupture or burst. Burst pressure is determined by such factors as the wall thickness and tensile strength of the balloon material.
High pressure balloons are desirable because they have the ability to exert more force and “crack” hard lesions. High pressure balloons are useful in high pressure procedures, such as Percutaneous Transluminal Angioplasty (PTA) in the peripheral vasculature, including the iliac, femoral, ilio-femoral, popliteal and renal arteries, and for the treatment of obstructive lesions of native or synthetic arteriovenous dialysis fistulae. High pressure balloons are also useful in stent deployment.
A biocompatible metal stents are often used to prop open blocked coronary arteries and to keep them from re-closing after balloon angioplasty. In an exemplary procedure, balloon of appropriate size and pressure is first used to open the lesion. The process is then repeated with a stent crimped onto a high pressure balloon. The stent is deployed when the balloon is inflated. A medium to high pressure balloon is preferable for stent deployment because the stent must be forced against the artery's interior wall so that it will fully expand, thereby precluding the ends of the stent from projecting into the arterial channel, which may inhibit flow there through and encourage the formation of thrombus.
High pressure balloon materials are typically stiffer than conventional medium or low pressure balloon materials. Whereas medium or low pressure balloons use materials such as polyethylene, high pressure balloons use materials such as Nylon 12 or PET. See, for example, U.S. Pat. No. 4,490,421, U.S. Pat. No. Re. 32,983, U.S. Pat. No. Re. 33,561, and EP 0135990, which are incorporated herein by reference in their entirety, which disclose a high molecular weight, biaxially oriented, flexible, polymeric balloon with a tensile strength of at least 31,714 psi (218.86 MPa), which can be made of PET. See, also, U.S. Pat. No. 5,264,260, which discloses a PET balloon, optionally melt blended or mixed with other polymeric or nonpolymeric materials, having an intrinsic viscosity of less than or equal to 0.6 dl/g and a calculated radial tensile strength greater than about 25,000 psi (172 MPa), and is also incorporated by reference in its entirety.
In general, improvements have been made to conventional high pressure balloons over the years. However, because these balloons are subject to the application of high pressure, these balloons are still prone to puncture or tearing, such as circular tearing of the balloons under burst pressure. Moreover, when these balloons burst in a constricted state, they often tear along a circumferential path that may lead to separation of the balloon into two or more pieces. As a consequence, forceps or other device may need to be inserted into a patient to remove the balloon pieces thus requiring more complicated and/or longer procedures.
As such, there still exists a need in the industry for high pressure balloons which display improved puncture and tearing resistance, when compared to the conventional high pressure balloons, while maintaining sufficient burst strength.